1. Field of the Invention
The present invention relates to electronic detection devices. More specifically, it relates to a device that can be interconnected with existing or new electrical control/indication circuits to monitor the continuity of circuits, without the need for additional cable or indicating devices, and to provide distinct indication of an abnormal condition. The control/indication circuits usually have an indication device comprised of indicating lights. The invention would, upon detection of an abnormal or open condition in the control circuit, provide a fixed oscillation frequency switching function in the existing indicator light(s) of the control/indication circuit to warn of the abnormal or open condition. When the control circuit is returned to normal state, the present invention will automatically reset. The device does not affect the control circuit being monitored under any condition.
The type of control/indication circuits addressed are those that would be present in various power production, chemical and other processes. There is a need to provide a means by which such control circuits can be monitored for an open Thermal Overload (TOL) relay contact condition. An open contact condition would render the control circuit inoperative. In some industries, it is critical to immediately identify and provide remote indication (at the control station) of an inoperative motor operated valve (MOV) control circuit (thus an inoperative valve) due to TOL trip. It is just as critical to provide continuous valve position indication if a TOL trip occurs. Different approaches have been taken to alert the operation personnel of this inoperative condition, but no one method provides a satisfactory solution to date. At best, various control/indication circuit design methods currently in use indicate, using separate alarm/indication circuits, loss of power to control circuits which could be due to other than a TOL trip condition.
In retrofit and in new circuits, design methods require additional indication and/or alarm circuits and cables between the MOV and control stations to provide positive indication of an abnormal condition. Circuit designs using existing indicating lights either do not provide a positive indication of an abnormal condition or they affect the ability of the lights to perform their original design intent (i.e. valve position indication).
At present, there does not appear to be any known single device;
(1) to detect and provide a distinct visual alarm, using existing indication lights in the circuit, when the control circuit is rendered inoperative due to an open contact; PA0 (2) to test the device circuitry in its passive state (i.e. normal) without affecting the control and indication circuits; PA0 (3) to provide device protection circuitry to separate it from the voltage of the monitored circuit; PA0 (4) to provide light at the device to indicate power is available to the device in its passive state; and PA0 (5) to provide distinct visual indication at the device when it is in its active state indicating an abnormal state of the monitored control circuit.
2. Description of the Prior Art
The following patents and inventors are felt to be related to, but do not disclose, either singly or in combination, the applicants' unique invention.
U.S. Pat. No. 1,725,022 issued to Stacey et al. discloses a voltage comparison system in which the alarm feature involves the lighting of a lamp should a problem arise.
U.S. Pat. No. 3,648,103 issued to Okada discloses an alarm system that comparatively measures an inputted voltage. An abnormal condition will cause a neon lamp to flash, thereby notifying an operator of the problem.
U.S. Pat. No. 4,247,849 issued to Morris et al. discloses an industrial plant alarm device that provides an LED indication of an unacceptable voltage problem.
U.S. Pat. No. 4,694,372 issued to Sibeud discloses an alarm system which measures the differences in voltage and provides a visual flashing alarm.